Colloid transfer activator containing a formaldehyde generating compound



United States Patent U.S. Cl. 96*28 6 Claims ABSTRACT OF THE DISCLOSURE An alkaline activator solution for use in developing a substantially unhardened silver halide emulsion in the presence of a tanning developing agent, which activator solution contains free formaldehyde or also a formaldehyde donor and which also may contain a hydrolysis product of the formaldehyde donor.

This application is a continuation-in-part of U.S. patent application Ser. No. 505,024, filed Oct. 24, 1965 now abandoned which is a continuation-in-part of U.S. patent application Ser. No. 285,570, filed June 5, 1963 now abandoned.

This invention concerns activators for use with unhardened photographic emulsions to obtain offset printing plates and to facilitate the production of multiple copies in colloid transfer processes.

In the colloid transfer processes, an image in soft adhesive organic colloid is formed photographically and a discrete stratum of the image is transfer-red to a receiving sheet to provide a reproduction of the subject. This process is described in Ytuzy et al., U.S. Patents 2,596,756, issued May 3, 1952 and 2,716,059, issued August 26, 1955, and embodies the exposure to a subject of a substantially unhardened gelatino-silver halide emulsion layer, which may contain a gelatin tanning silver halide developing agent as Well as a non-tanning silver halide developing agent.

Upon activation of the exposed gelatino-silver halide emulsion with an alkaline solution in the presence of the developing agent or agents, tanning development of the most exposed regions of the emulsion corresponding to the highlights of the subject proceeds, although some development of the less exposed regions also takes place to provide visual density for the transferred image as explained in U.S. Patent 2,716,059 above. Thereafter, the developed emulsion is pressed into contact with an absorbent receiving sheet to cause the less exposed regions and less developed regions of the emulsion to adhere to the receiving sheet. Subsequently, when the emulsion and receiving sheet are separated, a stratum of the less exposed regions of the emulsion remains on the sheet and appears as a positive silver image of the original subject.

In the preparation of offset printing plates, an unhardened emulsion of the type described above can be used to provide an image on a support which can be used for offset printing purposes. Typical processes of this type are described in Clark et al., U.S. Patent 2,763,553, issued Sept. 18, 1956 and Lake et al., U.S. Patent 2,794,388, issued June 4, 1957.

In carrying out the colloid transfer process, the exposed unhardened emulsion is immersed in an alkaline activator solution which causes development of the most exposed regions and tanning in these areas. The mechanism of the colloid transfer depends upon the unhardened areas of the emulsion transferring to the receiver sheet when the 3,464,821 Patented Sept. 2, 1969 "ice emulsion is pressed in contact therewith. However, the transferred image areas are of unhardened gelatin and relatively soft in nature so that in some instances too much unhardened gelatin is transferred to the support for satisfactory use in lithographic printing plates. Accordingly, it has been desirable to find an activator solution which would provide satisfactory activation of the emulsion so that a regulated amount of the unhardened areas of the unexposed emulsion Would be made to adhere to a receiving sheet.

Moreover, the alkaline activator solutions which are commonly used have a temperature latitude of about 8l83 F. to obtain satisfactory lithographic plates or copies. At higher temperatures, a fuzzy image may result due to bleeding. This means that a controlled environment is desirable in order to obtain the optimum results.

Accordingly, it has been desirable to find an activator which would be useful for colloid transfer emulsions which would provide a transferred image particularly suitable for lithographic use having good definition, smoothness with proper contrast, good inking rate, satisfactory offset quality and long press life without emulsion picking. Moreover, the activator should have greater temperature latitude, preferably operating ranges as high as 93-96 F.

We have found an activator and a method of improving conventional activators which provide improved lithographic plates from colloid transfer materials as well as improving the operating temperature range of activators for use in making lithographic plates.

One object of the invention is to provide an alkaline activator solution which will provide satisfactory lithographic plates from colloid transfer emulsions. Another object is to provide an activator having an operating working temperature up to about 96 F. A further object is to provide an improved lithographic plate from a colloid transfer process having uniform photographic characteristics. An additional object is to provide a method of processing colloid transfer materials which results in an image having a good inking rate and good offset quality. A still further object is to provide a method of regulating the amount of unhardened gelatin transferred in the colloid transfer processes.

The objects of the invention are attained by employing alkaline activator solutions containing from about 30 to 250 mgs. of formaldehyde per liter, or formaldehyde and a sufficient amount of a donor for formaldehyde to yield or maintain this concentration of formaldehyde in the solution. The formaldehyde donor compounds, described in more detail below, are compounds which are capable of hydrolysis in the presence of alkali to yield formaldehyde. It is advantageous to also add to the activator solution a further quantity of the hydrolysis product of certain formaldehyde donor compounds to aid in maintaining the above concentration of the formaldehyde in the activator solution.

The following are representative formaldehyde donors which are hydroylzed with alkali to produce formaldehyde for control of the colloid image transfer:

Mgs./ 1. (1) 2- (hydroxymethyl)-2-nitro-1,3-propanediol 500 (2) 2-methyl-2-nitro-1,3-propanediol 750 (3) 2-ethyl-2-nitro-l-propanediol 750 (4) Z-methyI-Z-nitro-l-propanol 3,000 (5) sodium formaldehyde bisulfite 1,300 (6) 3-,B-hydroxyethyloxazolidine 0 (7) 3-phenyloxazolidine 1,000 (8) Oxazolidine 10,000 (9) 3-methyloxazolidine 400 (1 0) Methylenebisoxazolidine 400 (11) S-ethyloxazolidine 500 The data following each name will be discussed below.

A useful group of the above formaldehyde donor compounds is, therefore, the 2-nitro-1,3-propanediols soluble in aqueous alkaline solutions and capable of hydrolysis in the alkaline activators to produce formaldehyde. To undergo this reaction most effectively, the carbon atom in the 2-position should be further substituted with,'-for example, hydroxyalkyl, lower alkyl, phenyl, substituted phenyl and the like. The hydrolysis of these compounds to produce formaldehyde is believed to proceed as follows:

(Z-hydroxymethyD-Z- 2nit-ro-1,3-propancdiol nitro-l,3-propauediol The above list of compounds also illustrates the important oxazolidine class of the donor compounds which are soluble in aqueous alkaline solution and are hydrolyzed in the alkaline activator solutions to yield formaldehyde for control of the transfer of the colloid images. The hydrolysis of the oxazolidines in the alkaline activator solutions is believed to proceed as illustrated in the following reaction:

Hornor-n H2O on. cm 2 N-II HCIIO 1 or-r2NornornoH OH no crncrn 3-dhydroxyethyloxazolidine Imiuodiethanol It will be seen that the reaction is reversible but tends to proceed to the right. Therefore, the amount of formaldehyde produced in the reaction is controlled primarily by the amount of oxazolidine compound initially present in the alkaline activator solution. However, we have found that when the oxazolidines are used, the production of the formaldehyde therefrom can be suppressed or controlled as desired by the incorporation of additional quantities of the hydrolysis product, preferably of the same oxazolidine compound, e.g. iminodiethanol, into the alkaline activator. Thus, by use of substantial amounts of the hydrolysis product in the activator the formaldehyde can be produced at substantially the rate it is consumed in the development and colloid transfer steps of the process. Accordingly, it is possible to add substantially larger amounts of the formaldehyde donor compound to the alkaline activator than would otherwise be the case. The result is that the capacity of the activator to provide formaldehyde at the desired level is greatly increased. Since the reaction involving the propanediols is not reversible the production of formaldehyde is controlled primarily by the amount of the propanediol present in the activator solution. Addition of further amounts of the hydrolysis product of the propanediols does not materially aid in suppressing the formation of formaldehyde.

The amount of formaldehyde donor compound used in the activator solutions depends upon the activity of the individual compound, e.g. the ease of hydrolysis of compound, upon the concentration of formaldehyde to be maintained in the solution in the range of 30250 mgs./liter, whether or not additional amounts of the hydrolysis product have been added and whether few high density prints are desired of more prints of medium density. Thus, up to about 40 gms./liter of the oxazolidine donor can be used if sufficient hydrolysis product is present to control the production of the formaldehyde. In the above table, the grams per liter shown opposite the name of the formaldehyde donor compounds 1-11 represents the optimum amount of the compound to be added to a typical activator composition containing 3% sodium salicylate (a gelatin softener), .090 g. formaldehyde and 7% potassium phosphate, to obtain about four good copies of the original. In absence of the donor compound only one good high density print was obtainable with the photographic emulsion being used. As will be seen from the table, 10,000 mgs. of oxazolidine per se was required, presumably because it is slow to hydrolyze. Thus, lower amounts of the other oxazolidines can be used to provide the mentioned concentration of formaldehyde.

The concentration of the hydrolysis product of the oxazolidines in the activator solutions depends primarily upon the concentration of formaldehyde (in the range of 30-250 rngs./liter) to be maintained in the solution, upon the amount and type of the formaldehyde donor compound present, and the number and density of the copies desired. For example, in the formula shown in Example 6 below, 20 gms./l. of iminodiethanol were useful with 10 gms./l. of the parent oxazolidine compound. An increase in the concentration of the inimodiethanol can be expected to allow the transfer of fewer colloid images each having a high density. Conversely, use of a lower concentration of the iminodiethanol results in the production of more formaldehyde and, thus, more copies of lower density. However, if the same activator formula contains no iminodiethanol, less than 2 gms. of the oxazolidine can be used, otherwise excessive formaldehyde is produced. It is usually not necessary to use more than about 60 gms. of the iminodiethanols per liter of activator solution. Simple experiments with a given alkaline activator solution will show the optimum ratio and concentrations of the other oxazolidines and hydrolysis products to use.

The formaldehyde containing activator solutions may contain as the source of alkali inorganic alkali such as alkali metal carbonates, hydroxides or phosphates, eg sodium and potassium carbonates and hydroxides and trisodium phosphate. Amines such as Z-diethylaminoethanol (not to be confused with the above iminodiethanol compound) are useful. The pH of the solutions can range from about l0l3 which is adequate to effect fast development of the emulsion layer.

Gelatin softeners can also be added to the activator solutions to aid in control of the image transfer, for example, the amounts used will vary with the gelatin hardening capacity, e.g. in the case of sodium salicylate 30 gms./l. is useful.

A sequestering agent, such as ethylenediarnine tetraacetic acid sodium salt, can be used in the activator solutions, e.g. up to about 5 gms./l.

It is usually desirable to package the activators in concentrated form in a multi-package system, eg a first package containing formaldehyde or also the formaldehyde donor and a second package containing the alkali and if desired, hydrolyzed formaldehyde donor such as iminodiethanol, gelatin softeners, e.g. sodium salicylate and sequestering agent. For use, the two packages are mixed and the required amount of water added to provide a working solution.

It will be appreciated that while these activator solutions containing formaldehyde are very useful for providing improved lithographic printing plates, the activators can also be used for making copies accordng to the colloid transfer process in the customary manner. The activators have a relatively long tank life of about 4 to 6 months and can be replenished merely by adding more of the same activator or by adding one or more of the components of the activator from time to time.

While our invention involves the incorporation of small amounts of formaldehyde into the activator, in certain instances the formaldehyde donor may be incorporated in the colloid process silver halide emulsion. A very small amount of formaldehyde donor incorporated into the substantially unhardened silver halide emulsion unexpectedly improves the number of copies obtained in certain instances employing document copy methods.

The following examples are intended to illustrate our invention but not to limit it in any way.

EXAMPLE 1 An activator for the colloid transfer process was prepared by mixing the following components:

Components: Grams per liter Z-diethylaminoethanol 40 NaHCO Ethylenediamine tetraacetic acid (disodium salt) Sodium salicylate 5.0 2-hydroxymethyl-2-nitro-1,3-propanediol 0.33

Sufiicient water was added to bring the volume to one liter.

The activator as prepared above was used in a colloid transfer process of the type described in Yutzy et al. US. Patent 2,596,756. When the exposed silver halide emulsion containing a tanning developer and a non-tanning developer was immersed for 6 seconds and while still wet, pressed in contact with a receiving sheet, a good quality print was obtained by transfer of the unexposed areas. The temperature of the activator was 83 F. The transferred image was then immersed in an image conditioner to improve the wetting properties of the paper base and the inking properties of the image.

The image conditioner had the following composition:

The printing plate was a good photographic reproduction and when used directly in a lithographic printing press was found to be satisfactory for offset use. The image readily accepted greasy printing ink and had good reproducing characteristics. A thousand copies were prepared, indicating good press life.

EXAMPLE 2 Activator solutions were prepared with sufficient water to make one liter of solution having the following compositions:

Grams per liter C omponents 2-diethylaminoethanol Sodium salicylate 2-(hydroxymethyD-2-nitro propanediol Sodium bicarbonate Ethylenediamine tetraacetic acid (disodium salt) These activators, used to activate silver halide emulsions of the type described in US. Patents 2,763,553 and 2,794,388 containing a tanning developer, were found to have good offset printing characteristics at temperatures from 8096 F.

EXAMPLE 3 An activator for the colloid transfer process was prepared by mixing the following components:

Components: Grams per liter Potassium phosphate (tribasic) 70 Sodium salicylate Ethylenediamine tetraacetic acid (disodium salt) Formaldehyde 0.09

Sufficient water was added to bring the volume to one liter.

The activator, as prepared above, was used in a colloid transfer process of the type described in Yackel and Smith EXAMPLE 4 An activator for the colloid transfer process was prepared by mixing the following components:

Components: Grams per liter Phosphoric acid 37.5

Cinnamic acid 25 1,5-naphthalenedisulfonic acid (disodium salt) 2O Ethylenediamine tetraacetic acid (disodium salt) 3-methyloxazolidine 1.5

The activator was diluted to one liter and used as in Example 3. Similar results were obtained.

EXAMPLE 5 An activator for the colloid transfer process was prepared by mixing the following components:

Components: Grams per liter Potassium carbonate 5S Cinnamic acid 45 Ethylenediamine tetraacetic acid (disodium salt) 1 3- fl-Hydroxyethyloxazolidine l0 Iminodiethanol 20 Adjust pH to 11.6 with 45% KOH. Water to 1 liter.

The above activator was used as in Example 3 with similar results.

EXAMPLE 6 Suflicient 2 (hydroxymethyl)-2-nitro-l,3-propanediol was added to a sample of colloid transfer emulsion described in Example 1 of Yackel et al. U.S. Patent 3,240,599 to bring the concentration to 0.01% by weight. The emulsion was coated on a polyethylene coated paper support. When the emulsion was processed in the colloid transfer process, several good copies were obtained.

EXAMPLE 7 An activator having wide temperature latitude was prepared as follows:

Grams K3PO4 (31111.) Cinnamic acid 45 KOH 63 pHll.60. Ethylenediamine tetraacetic acid tetrasodium salt 4 3-B-hydroxyethyloxyazolidine 3 Water to 2 liters.

This activator when used as in Example 2 was found to provide satisfactory copies at temperatures from 7 0-96 F.

EXAMPLE 8 Activators are prepared as in Example 7 using a sufficient amount of the other oxazolidines listed above in place of 3-/8-hydroxyethyloxazolidine to provide about 30- 250 mgs. formaldehyde per liter of activator with similar satisfactory results.

By an unhardened silver halide emulsion we mean one that is not harder than a gelatin layer containing about 0.7 g. of formaldehyde per pound of gelatin freshly coated.

The silver halide sensitized sheet may be exposed by projection or contact printing methods under a two-tone subject such as a line or half-tone transparency or printed matter. If desired, reflex exposure methods may be used for making the exposure. The support, to which the unhardened stratum is transferred, is preferably a paper stock which has thereon a gelatin overcoat. However, other surfaces may be used to receive the transferred image, including metal plates, polymeric plates and the like, for example, in preparing printing plates as described in U.S. Patents 2,763,553 and 2,794,388.

While development in the above activator solutions is proceeding, light should be excluded to the extent required by the particular silver halide present in the emulsion. With daylight working emulsions, limited exposure to roomlights may be given during the exposure and development steps. Other emulsions may require the use of the usual safelights during the exposure and processing steps. When the proper amount of exposure has been given, gelatin tanning silver halide development occurs principally in the more highly exposed areas of the emulsion and little or no tanning development in the other areas.

When development is complete as determined by trial with the particular emulsion in conditions of operations and use, the sensitive element is pressed into contact with the receiving material such as paper by means of a squeegee blade or rollers. Immediately thereafter, the sensitive element and receiving support are separated, leaving a stratum of the less exposed and thus less hardened regions of the emulsions adhering to the receiving sheet.

In a preferred embodiment of the invention, the tanning developing agent and non-tanning developing agent are present in the emulsion. However, the tanning and/or the non-tanning developing agents may be present in the alkaline activator solution or if only one is in the activator the other may be in the emulsion. A very useful combination of developing agents is 4-phenyl catechol with 4- methoxy-a-naphthol. Since the latter is self-coupling, it forms a colored compound during developing which contributes density to the print. Other useful tanning and nontanning silver halide developing agents are disclosed in the above patents.

A useful image conditioner which can be used for treating the transferred image on the printing plate comprises a mixture of a condensate of .2 to .6 mole of 2-furaldebyde with 1 mole of resorcinol, tannic acid, 1,3-diethyl- 2-thiourea, glycerol, ethyl alcohol, glacial acetic acid and water. At least 10% of the concentrate is used. Other useful proportionate ranges are as follows:

Grams per 500 grams Water to make 500 grams of final solution.

The image conditioner may be applied by any convenient method such as swabbing the image, immersing in a conditioner bath or the like. The Z-furaldehyde and resorcinol condensate can be prepared by dissolving the resorcinol in warm water, cooling to room temperature and adding the 2-furaldehyde. A small amount of sodium hydroxide is added and the reaction permitted to continue until the condensate is formed. The remaining components of the image conditioner can then be added to the reaction solution without separating the condensate.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. An aqueous activator solution adapted for use in the development of a substantially unhardened gelatinosilver halide emulsion layer in the presence of a tanning silver halide developing agent, consisting essentially of alkali and an amount of a 2-nitro-1,3-propanediol or oxazolidine formaldehyde donor compound capable of hydrolysis in the presence of the alkali to yield from about 30-250 mgs. of free formaldehyde per liter of the activator solution.

2. The activator solution of claim 1 wherein the donor compound is 2- (hydroxymethyl)-2-nitro-1,3-propanediol.

3. The solution of claim 1 further containing a gelatin softening agent.

4. The activator solution of claim 1 wherein the donor compound is 3-5-hydroxyethyloxazolidine.

5. The activator solution of claim 1 wherein both 3-,8- hydroxyethyloxazolidine and iminodiethanol are present to maintain the concentration of formaldehyde.

6. In a photographic organic colloid transfer process wherein an unhardened gelatino-silver halide emulsion layer containing a gelatin tanning silver halide developing agent is activated with alkaline solution and the less developed portions of the emulsion layer are transferred to a receiving sheet, the step of activating the emulsion layer by means of an aqueous activating solution consisting essentially of alkali and an amount of a 2-nitro-1,3-propanediol or oxazolidine formaldehyde donor compound capable of hydrolysis in the presence of the alkali to yield from about 30250 mgs. of free formaldehyde per liter of the activator solution.

References Cited UNITED STATES PATENTS 2,364,017 11/1944 Baldsiefen 96-111 X 2,494,055 1/1950 Orkin 96-111 3,043,688 7/1962 Weyerts et a1. 96-28 3,189,449 6/1965 Yost 96-28 2,227,982 1/1941 Sheppard et al. 106-125 X 2,708,169 5/1955 Keil et a1. 106-125 X NORMAN G. TORCHIN, Primary Examiner R. E. FIGHTER, Assistant Examiner U.S. Cl. X.R. 96-111 

